Tunable laser sources are applicable to a number of diagnostic and therapeutic medical applications. Optical coherence tomography is used to provide spatial resolution, enabling the imaging of internal structures. Spectroscopy is used to characterize the composition of structures, enabling the diagnosis of medical conditions, by differentiating between cancerous, dysplastic, and normal cellular structures. Fluorescence and exogenous chromospores can be used to increase the signal to noise ratio in these processes, providing for more accurate diagnostics.
For example, in one configuration for spectroscopy, the tunable laser source is used to scan a spectral band of interest, such as a scan band in the near infrared or 850 nanometers (nm) to 1–2 micrometers (μm), for example. The generated light is used to illuminate tissue in a target area. Diffusely reflected light resulting from the illumination is then collected and transmitted to a detector. By correlating the scanning of the tunable laser source to the time varying response of the detector, the spectral response of the target area tissue can be resolved. Statistical techniques can be further used to extract useful information from even low-resolution spectral data. For example, chemometrics, which combines spectroscopy and mathematics, can provide clear qualitative as well as quantitative information.
One specific example of an application for spectroscopy concerns the diagnosis of atherosclerosis. This is an arterial disorder involving the intimae of medium- or large-sized arteries, including the aortic, carotid, coronary, and cerebral arteries. Atherosclerotic lesions or plaques contain a complex tissue matrix, including collagen, elastin, proteoglycans, and extracellular and intracellular lipids with foamy macrophages and smooth muscle cells. In addition, inflammatory cellular components (e.g., T lymphocytes, macrophages, and some basophiles) can also be found in these plaques. Efforts are being made to spectroscopically analyze blood vessel walls in vivo using infrared wavelengths to identify and assess the compositions of atherosclerotic lesions.